How to convert a mesh model to a curve/surface?
In Blender 2.79 you may consider 'shrink wrapping' a NURBs surface to your mesh.

Add a NURBS Surface into your scene above or beside a meshed object of interest (your ship hull) when in object mode. Select the NURB surface and go into Edit Mode, then subdivide as needed to get a suitable resolution for your needs, and perhaps scaling so that the NURBs surface would fully cover your mesh when shrink wrapped. Return to object mode and apply an object modifier in the deform category called Shrinkwrap. Choose the project option with a suitable direction until you get the NURBs surface to fully project on your mesh. 

You could apply the result if needed so that the NURB surface retains the ship hull shape for export by pressing the Apply button in the object modifier interface. You could safely delete the ship mesh and the NURB would retain the hull shape.

- Ed -